The sedimentary layers of Earth increase in temperature with depth. The massive weight of these layers also causes an increase in pressure which increases the temperature even more. This cycle of heat and pressure transforming the existing rock is called the rock cycle, a system of constantly changing rock formation and melting that links sedimentary, igneous, and metamorphic rock. The hotter the temperature and pressure the greater the metamorphic changes. Depending on the conditions under which rock is changed, the rock gradient forms new metamorphic rock into high-grade or low-grade metamorphic rock